1. Field of the Invention
This invention relates to tube pullers for gripping and removing tubes from surrounding structures. It is particularly useful in removing heat exchanger tubes from tubesheets for subsequent metallurgical evaluation.
2. Description of the Prior Art
Tube grippers for gripping and pulling tubes out of tubesheets are known in the prior art. Typically, such tube grippers include an expandable jaw which may be inserted into the open mouth of the tube. Such expandable jaws usually include a plurality of gripping teeth on their outside surfaces which grip the inside walls of the tube when the jaw is expanded. Thereafter, a hydraulic ram or an equivalent pulling means pulls the tube from its tubesheet.
While such tube pullers are able to satisfactorily remove tubes from tubesheets in a variety of applications, they are seriously deficient in maintaining the metallurgical properties of the tubes they withdraw. This is a particularly serious drawback in nuclear steam generators, where samples of heat exchanger tubes must be periodically withdrawn through the tubesheet separating the primary water system from the secondary water system in order to determine whether or not the tubes in that particular steam generator are afflicted with corrosion degradation. The mouth of such a tube is typically expanded between two and four inches into the tubesheet; the frictional force between such a tube and its tubesheet is so great that a tensile force as high as 10 metric tons may be required to pull the sample tube out from the tubesheet. If the exterior walls of the tube have been degraded and weakened by corrosion, the tensile force required to pull an expanding jaw of a conventional tube puller may cause the tube to break, thereby making it difficult, if not impossible, to determine the exact degree to which the wall of the sample tube was weakened by corrosion degradation. Even if the tensile force which the expanding jaw applies to the mouth of the tube is not sufficient to actually break the tube, the application of such a large tensile force across the cross-section of the tube walls will, at the very least, distort the metallurgical properties of the tube by exacerbating any flaws the tube may have along its radius.
Clearly, a need exists for a tube puller which is capable of quickly and effectively gripping and pulling the tubes in tubesheets without distorting the metallurgical properties of these tubes in the regions sought to be examined.